An automated guided vehicle system is known which is used in a semiconductor manufacturing plant or the like and which comprises a moving path laid along processing devices or the like and on which an automated guided vehicle automatically runs. The automated guided vehicle conveys work pieces. The automated guided vehicle system is desired to accurately stop the automated guided vehicle in front of a processing device. The automated guided vehicle is configured as described below.
FIG. 9 is a diagram schematically showing the configuration of a conventional automated guided vehicle system. Processing devices 104, 104, . . . are arranged along a running path 102 for an automated guided vehicle (hereinafter referred to as “guided vehicle”) 101. Stop position markers 120 are applied to positions at which the guided vehicle 101 is to be stopped, such as the processing devices 104, 104, . . . The guided vehicle 101 is provided with a marker detecting sensor 115 that detects the stop position markers 120.
When a destination (a processing device 104 or the like) is specified, a running program in which timings for acceleration and deceleration and the like are written is created for the guided vehicle 101. Then, the running of the guided vehicle 101 is controlled in accordance with the running program. The guided vehicle 101 is provided with an encoder on a rotating shaft of wheels. Output pulses from the encoder are counted to accumulate the distance that the guided vehicle 101 has run. When nearing the target processing device 104, the guided vehicle 101 starts to be decelerated (see FIG. 9A). The speed is sufficiently reduced, so that the guided vehicle 101 runs at an about-to-stop speed at which it can be immediately stopped at any time (see FIG. 9B). When the marker detecting sensor 115 detects the tip of the stop position marker 120 at the destination (see FIG. 9C), the output pulses from the encoder newly start to be counted. When the marker detecting sensor 115 reaches the center of the stop position marker 120 in its longitudinal direction, the wheels of the guided vehicle 101 are stopped (see FIG. 9D). The stop of the guided vehicle 101 is controlled as described above so that the guided vehicle 101 can be accurately stopped at the destination.
However, during running, the wheels of the guided vehicle 101 may slip on the running path 102. In particular, a slip is likely to occur while the guided vehicle 101 is being accelerated or decelerated. If such a slip occurs, there may be a difference between the running distance obtained by accumulating the output pulses from the encoder and an actual running distance. As a result, the guided vehicle 101 may start to decelerate earlier than scheduled and reach the about-to-stop speed in front of and relatively away from the destination. Then, the guided vehicle 101 carries out creep running at the about-to-stop speed until it reaches the destination. However, such an approach to the destination takes a very long time. Thus, the conventional system disadvantageously suffers a heavy time loss and fails to perform operations easily and efficiently.
In view of these points, the Unexamined Japanese Patent Application Publication (Tokkai) 2002-351541 discloses an automated guided vehicle improved as described below. As shown in FIG. 10, a large number of markers 220, 220, . . . are applied along a running path 202 for the guided vehicle 201. The markers 220, 220, . . . are applied not only to positions corresponding to the processing devices 204, 204, . . . but also to the positions between the processing device 204 and the processing device 204. The guided vehicle 201 is provided with a marker detecting sensor 215 to detect the markers 220. The speed of the guided vehicle 201 is controlled in accordance with the running path 202 until the marker 220 located at a position 207 immediately in front of a target stopped position 208 is reached. Between the stopped position 208 and the position 207 immediately in front of the stopped position 208, the speed and the deceleration start position are controlled on the basis of the distance to the stopped position 208.
When a destination (a processing device 204 or the like) is specified, the guided vehicle 201 runs at a speed specified by a running program until the marker 220 located at the position 207 immediately in front of the stopped position 208 corresponding to the destination is detected. As shown in FIG. 10A, when the marker detecting sensor 215 of the guided vehicle 201 detects the terminal of the marker 220 located at the position 207 immediately in front of the target stopped position 208, a pulse count value from an encoder provided on a rotating shaft of wheels of the guided vehicle 201 is preset to 0 (zero). That is, the terminal of the marker 220 is used as a reference position for the pulse count from the encoder. Then, the speed is controlled by counting output pulses from the encoder to accumulate the running distance of the guided vehicle 201 from the terminal of the marker 220 located at the position 207 immediately in front of the stopped position 208. When the guided vehicle 201 reaches a preset deceleration start position, deceleration control is performed to obtain a predetermined deceleration in order to accurately stop the vehicle at the stopped position 208.
As shown in FIG. 10B, the guided vehicle 201 nears the target stopped position 208 and detects the marker 220 provided at the stopped position 208. Then, the pulse count value from the encoder is preset again. The stop control of the guided vehicle 201 starts to be performed when the tip of the marker 220 located at the stopped position 208 is detected. The counting of pulses from the encoder is newly started at the tip of the marker 220 located at the stopped position 208. The running speed of the guided vehicle 201 is controlled to further decrease by accumulating the running distance. Then, as shown in FIG. 10C, the wheels of the guided vehicle 201 are stopped at the position at which the marker detecting sensor 215 detects the terminal of the marker 220 located at the stopped position 208. Consequently, the guided vehicle 201 is accurately stopped at the stopped position 208.
With the latter conventional technique (the Unexamined Japanese Patent Application Publication (Tokkai) 2002-351541), there is only a short distance between the stopped position 208 and the position 207 immediately in front of the stopped position 208. Accordingly, between the stopped position 208 and the position 207 immediately in front of the stopped position 208, there is only a small difference between the actual running distance and the running distance obtained by accumulating the output pulses from the encoder after the detection of the terminal of the marker 220 located at the position 207 immediately in front of the stopped position 208. This technique also substantially prevents the approach to the destination from disadvantageously requiring a long time as a result of the premature start of deceleration, which may occur with the former conventional technique. With the latter conventional technique, the guided vehicle 201 moves quickly between the stopped position 208 and the position 207 immediately in front of the stopped position 208. Furthermore, the guided vehicle 201 can be accurately stopped at the stopped position 208.
However, such stop control can be performed only on the stopped positions 208, 208, . . . If the guided vehicle 201 is stopped in a different place, problems similar to those with the former conventional technique may occur. Moreover, when the layout of the automated guided system is changed or new facilities are added, the markers 220, 220, . . . must be reapplied to desired positions in the changed system. Then, the guided vehicle 201 must be taught to stop at the positions of the reapplied markers 220, 220, . . . Subsequently, the guided vehicle 201 must be experimentally run to check whether or not it accurately stops at the positions of the markers 220, 220, . . . This checking operation requires much time and effort and is cumbersome. The prior art should also be improved in this point.
In view of these points, it is an object of the present invention to provide a moving body system which can determine a moved position of a moving body such as a guided vehicle or a stacker crane wherever it is on a moving path, which can stop the moving body anywhere, and which can quickly move the moving body to a stopped position.